Inactivation resistant factor VIII

ABSTRACT

The present invention provides novel purified and isolated nucleic acid sequences encoding procoagulant-active FVIII proteins. The nucleic acid sequences of the present invention encode amino acid sequences corresponding to known human FVIII sequences, wherein residue Phe309 is mutated. The nucleic acid sequences of the present invention also encode amino acid sequences corresponding to known human FVIII sequences, wherein the APC cleavage sites, Arg336 and Ile562, are mutated. The nucleic acid sequences of the present invention further encode amino acid sequences corresponding to known human FVIII sequences, wherein the B-domain is deleted, the von Willebrand factor binding site is deleted, a thrombin cleavage site is mutated and an amino acid sequence spacer is inserted between the A2- and A3-domains. Methods of producing the FVIII proteins of the invention, nucleotide sequences encoding such proteins, pharmaceutical compositions containing the nucleotide sequences or proteins, as well as methods of treating patients suffering from hemophilia, are also provided.

RELATED APPLICATIONS

The present application is a continuation application of U.S. Ser. No.09/819,098, filed on Apr. 11, 2001, which is a continuation of U.S. Ser.No. 08/980,038, filed on Nov. 26, 1997, which is a continuation-in-partof PCT International Application No. PCT/US97/06563, filed Apr. 24,1997, which claims the benefit of U.S. Provisional Application Ser. No.60/016,117, filed Apr. 24, 1996 and U.S. Provisional Application Ser.No. 60/017,785, filed May 15, 1996, all hereby expressly incorporated byreference.

SPONSORSHIP

Work on this invention was supported by the United States Governmentunder grants HL53777 and HL52173 awarded by the National Institutes ofHealth. The government may have certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates generally to procoagulant-active proteinsand more particularly, nucleotide sequences encoding factor VII proteincapable of secretion at levels higher than typically obtained withwild-type factor VII, APC resistant factor VII protein and inactivationresistant factor VIII protein.

BACKGROUND OF THE INVENTION

Human factor VIII:C (FVIII) is the coagulation factor deficient in theX-chromosome-linked bleeding disorder hemophilia A, a major source ofhemorrhagic morbidity and mortality in affected males. Traditionally,hemophiliacs were treated with transfusions of whole blood. Morerecently, treatment has been with preparations of FVIII concentratesderived from human plasma. However, the use of plasma-derived productexposes hemophiliac patients to the possible risk of virus-transmissiblediseases such as hepatitis and AIDS. Costly purification schemes toreduce this risk increases treatment costs. With increases in costs andlimited availability of plasma-derived FVIII, patients are treatedepisodically on a demand basis rather than prophylactically.Recombinantly produced FVIII has substantial advantages overplasma-derived FVIII in terms of purity and safety, as well as increasedavailability and accordingly, much research effort has been directedtowards the development of recombinantly produced FVIII. Due to thelabile nature of FVIII, especially following its activation, large andrepeated doses of protein whether plasma or recombinantly-derived, mustbe administered to achieve a therapeutic benefit. However, the amount ofFVIII protein the patient is exposed to has been correlated with thedevelopment of antibodies which inhibit its activity. In light of thisknown immunogenicity, one of the goals in developing new recombinantforms of FVIII for use as a therapeutic agent is the development ofproducts that reduce or eliminate such an immune response.

FVIII functions in the intrinsic pathway of blood coagulation as acofactor to accelerate the activation of factor X by factor IXa, areaction that occurs on a negatively charged phospholipid surface in thepresence of calcium ions. FVIII is synthesized as a 2351 amino acidsingle-chain polypeptide having the domain structure A1-A2-B-A3-C1-C2.Wehar, G. A. et al., Nature 312:337-342 (1984) and Toole, J. J. et al.,Nature 312:342-347 (1984). The domain structure of FVIII is identical tothat of the homologous coagulation factor, factor V (FV). Kane, W. H. etal., PNAS (USA) 83:6800-6804 (1986) and Jenny, R. J. et al., PNAS (USA)84:4846-4850 (1987). The FVIII A-domains are 330 amino acids and have40% amino acid identity with each other and to the A-domain of FV andthe plasma copper-binding protein ceruloplasmin. Takahashi, N. et al.,PNAS (USA) 81:390-394 (1984). Each C-domain is 150 amino acids andexhibits 40% identity to the C-domains of FV, and to proteins that bindglycoconjugates and negatively charged phospholipids. Stubbs, J. D. etal., PNAS (USA) 87:8417-8421 (1990). The FVIII B-domain is encoded by asingle exon and exhibits little homology to any known protein includingFV B-domain. Gitschier, J. et al., Nature 312:326-330 (1984) and Cripe,L. D. et al., Biochemistry 31:3777-3785 (1992).

FVIII is secreted into plasma as a heterodimer of a heavy chain (domainsA1-A2-B) and a light chain (domains A3-C1-C2) associated through anoncovalent divalent metal ion linkage between the A1- and A3-domains.In plasma, FVIII is stabilized by binding to von Willebrand factor. Morespecifically, the FVIII light chain is bound by noncovalent interactionsto a primary binding site in the amino terminus of von Willebrandfactor. Upon proteolytic activation by thrombin, FVIII is activated to aheterotrimer of 2 heavy chain fragments (A1, a 50 kDa fragment, and A2,a 43 kDa fragment) and the light chain (A3-C1-C2, a 73 kDa chain). Theactive form of FVIII (FVIIIa) thus consists of an A1-subunit associatedthrough the divalent metal ion linkage to a thrombin-cleaved A3-C1-C2light chain and a free A2 subunit associated with the A1 domain throughan ion association (see FIG. 1A). Eaton, D. et al., Biochemistry 25: 505(1986); Lollar, P. et al., J. Biol. Chem. 266: 12481 (1991); and Fay, P.J. et al., J. Biol. Chem. 266: 8957 (1991). This FVIIIa heterotrimer isunstable and subject to rapid inactivation through dissociation of theA2 subunit under physiological conditions.

Previous transfection studies demonstrated that FVIII is 10-fold lessefficiently secreted than FV. The inefficient secretion of FVIIIcorrelates with binding to the protein chaperonin identified as theimmunoglobulin binding protein (BiP), also known as theglucose-regulated protein of 78 kDa (GRP78) (Munro, S. et al., Cell46:291-300 (1986)) within the lumen of the ER (Dorner, A. J. et al.,EMBO J. 4:1563-1571 (1992)). BiP is a member of the heat-shock proteinfamily that exhibits a peptide-dependent ATPase activity. Flynn, G. C.et al., Science 245:385-390 (1989). BiP expression is induced by thepresence of unfolded protein or unassembled protein subunits within theER. Lee, A. S., Curr. Opin. Cell Biol. 4:267-273 (1992) and Kozutsumi,Y. et al., Nature 332:462-464 (1988). It has been shown that high levelFVIII expression induces BiP transcription. Dorner, A. J. et al., J.Biol. Chem. 264:20602-20607 (1989). In addition, FVIII release from BiPand transport out of the ER requires high levels of intracellular ATP.Dorner, A. J. et al., PNAS (USA) 87:7429-7432 (1990). In contrast, ithas been found that FV does not associate with BiP and does not requirehigh levels of ATP for secretion. Pittman, D. D. et al., J. Biol. Chem.269: 17329-17337 (1994). Deletion of the FVIII-B-domain yielded aprotein that bound BiP to a lesser degree and was more efficientlysecreted. Dorner, A. J. et al., J. Cell Biol. 105:2665-2674 (1987). Toevaluate whether the FVIII B-domain was responsible for BiP interaction,FV and FVIII chimeric cDNA molecules were constructed in which theB-domain sequences were exchanged. Pittman, D. D. et al., Blood84:4214-4225 (1994). A FVIII hybrid harboring the B-domain of FV wasexpressed and secreted as a functional molecule, although the secretionefficiency of the hybrid was poor, similar to wild-type FVIII. Pittman,D. D. et al., Blood 84:4214-4225 (1994). This indicated that thedifference in secretion efficiency between FV and FVIII was not directlyattributable to specific sequences within the FVIII B-domain, the mostdivergent region between these homologous coagulation factors.

To determine whether specific amino acid sequences within FVIII A-domaininhibit secretion, chimeric proteins containing the A1- and A2-domainsof FVIII or FV were studied. The chimeric protein containing the A1- andA2-domains of FV was secreted with a similar efficiency as wild-type FV.The complementary chimera having the A1- and A2-domains of FVIII wassecreted with low efficiency similar to wild-type FVIII. These resultssuggested that sequences within the A1- and A2-domains were responsiblefor the low secretion efficiency of FVIII. An A1-domain-deleted FVIIImolecule was constructed and secretion was increased approximately10-fold compared to wild-type FVIII A2-domain-deleted FVIII. Expressionof the FVIII A1-domain alone did not yield secreted protein, whereasexpression of the FVIII A2-domain alone or the FV A1-domain or A2-domainalone directed synthesis of secreted protein. Secretion of a hybrid inwhich the carboxyl-terminal 110 amino acids of the A1-domain werereplaced by homologous sequences from the FV A1-domain (226-336 hybridFVIII) was also increased 10-fold compared to wild-type FVIII, however,the secreted protein was not functional, i.e. did not displayprocoagulant activity, and the heavy and light chains were notassociated. Marquette, K. A. et al., J. Biol. Chem. 270:10297-10303(1995). It would thus be desirable to provide a functional recombinantFVIII protein having increased secretion as compared to wild-type FVIII.It would also be desirable to provide a functional recombinant FVIIIprotein with increased secretion as well as increased specific activity.

FVa and FVIIIa are inactivated by Activated protein C (APC) in thepresence of phospholipid and CaCl₂ and APC-resistance has beenconsidered to be one of the major causes of hereditary thrombophilia.Dahlbäck, B. et al., PNAS (USA) 90: 1004 (1993). The molecular basis forthe APC-resistance was attributed to resistance to APC cleavage andinactivation. Dahlbäck, B. et al., PNAS (USA) 91: 1396 (1994). Previousstudies on the APC inactivation of FVIII noted the generation of a 45kDa fragment (Fulcher, C. A. et al., Blood 63: 486 (1984)) derived fromthe amino-terminus of the heavy chain and was proposed to result fromcleavage at Arg336. Eaton, D. et al., Biochemistry 25: 505 (1986). Whilethe light chain of FVIII is not cleaved by APC, multiple polypeptides,representing intermediate and terminal digest fragments derived from theheavy chain, have been observed. Walker, F. J. et al., Arch. Bioch.Biophys. 252: 322 (1987). These fragments result from cleavage sitelocations at Arg336, the junction of the A1 and A2 domain, at Arg562,bisecting the A2 domain, and a site at the A2-B junction, likely atArg740. Fay, P. J. et al., J. Biol. Chem. 266: 20139 (1991). APCcleavage of FVIII at residue 336 generates a 45 kDa fragment from theamino-terminus of the A1-domain and cleavage at residues 562 and 740generates a 25 kDa fragment from the carboxy-terminus of the A2-domain(see FIG. 1A).

Previous studies have demonstrated that the B-domain of FVIII isdispensable for FVIII cofactor activity. Genetically engineered FVIIImolecules that have varying degrees of B-domain deletion (BDD) yieldsecreted single chain FVIII species in which no intracellularproteolysis of the primary translation product is observed. These BDDFVIII mutants are advantageous because they are more efficientlyproduced in mammalian cells. Functional characterization of these BDDFVIII molecules demonstrated that FVIII cofactor activity is retained ifthrombin cleavage after Arg372, Arg740 and Arg1689 occurs. Therefore,any functional construction of FVIII genetically engineered thus fargenerates a FVIIIa heterotrimer following thrombin activation. Thefunctional advantages of previous BDD FVIII constructs has thereforebeen limited by rapid dissociation of the non-covalently linked A2subunit from FVIIIa.

It would thus be desirable to provide improved recombinant FVIIIprotein. It would also be desirable to provide FVIIIa protein that isresistant to activation. It would further be desirable to provide FVIIIaprotein that is APC-resistant. It would also be desirable to provideFVIII protein having increased secretion as compared to wild-type FVIII.It would further be desirable to provide FVIII protein having increasedsecretion and APC-resistance. It would also be desirable to provideFVIII protein having increased secretion and inactivation resistance. Itwould also be desirable to provide a method of treating hemophiliacpatients with improved recombinant FVIII. It would further be desirableto provide a method for treating hemophiliac patients via replacementtherapy, wherein the amount of FVIII protein required to treat thepatient is decreased.

SUMMARY OF INVENTION

The present invention provides novel purified and isolated nucleic acidsequences encoding procoagulant-active FVIII protein. In one embodiment,the nucleic acid sequences of the present invention encode amino acidsequences corresponding to known human FVIII sequences, wherein theA1-domain, specifically amino acid residue 309, phenylalanine, ismutated. In a preferred embodiment, Phe309 is either deleted orsubstituted with any other amino acid residue, preferably serine. Theresulting FVIII protein is capable of secretion at levels higher thantypically obtained with wild-type FVIII and retains procoagulantactivity.

In another embodiment, the nucleic acid sequences of the presentinvention encode amino acid sequences corresponding to known human FVIIIsequences wherein APC cleavage sites have been mutated. In a preferredembodiment, amino acid residues 336 and 562 are mutated preferably fromarginine to isoleucine and arginine to lysine, respectively. Theresulting FVIII protein is APC resistant and thus for convenience, isgenerally referred to herein as “APC resistant FVIII.”

In yet another embodiment, the nucleic acid sequences of the presentinvention encode amino acid sequences corresponding to known human FVIIIsequences wherein the B-domain is deleted, the von Willebrand factorbinding site is deleted, a thrombin cleavage site is mutated, and anamino acid sequence spacer is inserted between the A2- and A3-domains.In a preferred embodiment, the thrombin cleavage site Arg740 is mutated,preferably by substitution with alanine. In another preferredembodiment, the amino acid sequence spacer is the amino portion of theB-domain, preferably the 54 residues of the amino portion of theB-domain. In yet another preferred embodiment, one or both of the APCcleavage sites is mutated, as described herein. It has been surprisinglyfound that upon activation by thrombin, this protein is a heterodimer,wherein the A2-domain remains covalently associated with the light chain(see FIG. 1B). This heterodimer configuration is more stable than thewild-type heterotrimer configuration and has an approximate five-foldincrease in specific activity compared to purified wild-type FVIII.Thus, in a preferred embodiment, the FVIII of the present invention issecreted as a single-chain polypeptide which, upon activation bythrombin, achieves an inactivation resistant FVIII heterodimer. Forconvenience, this novel FVIII of the present invention is generallyreferred to herein as “inactivation resistant FVIII.”

In a further embodiment, the inactivation resistant FVIII of the presentinvention may be induced to bind to von Willebrand factor (vWF). It hasbeen found that in the presence of an anti-light chain antibody, ESH8,the inactivation resistant FVIII of the present invention, which lacksthe vWF binding site, has an increased binding affinity to vWF. Such anantibody or other cross-linking agent which induces binding to vWF may,therefore, be used to further stabilize the inactivation resistant FVIIIof the present invention.

In yet a further embodiment, the nucleic acid sequences of the presentinvention encode APC resistant FVIII amino acid sequences having amutation at residue 309, phenylalanine. Preferably, Phe309 is deleted orsubstituted with another amino acid, e.g., serine. The nucleic acidsequences of the present invention may also encode inactivationresistant FVIII amino acid sequences having a mutation at Phe309. Again,Phe309 is preferably deleted or substituted with another amino acid,e.g., serine. Thus, the nucleic acid sequences of the present inventionencode FVIII proteins that exhibit inactivation resistance and/orincreased secretion.

It will be appreciated to those skilled in the art that due to theinactivation resistance of the proteins of the present invention andaccompanying increased specific activity, a lower dosage of protein maybe administered to hemophiliac patients during FVIII replacementtherapy. Thus, by utilizing the proteins of the present invention, thetotal exposure of protein to the patient is reduced, thereby loweringthe likelihood of inhibitor formation. It will further be appreciatedthat the novel FVIII of the present invention will also be useful ingene therapy applications.

Additional objects, advantages, and features of the present inventionwill become apparent from the following description and appended claims,taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The various advantages of the present invention will become apparent toone skilled in the art by reading the following specification andsubjoined claims and by referencing the following drawings in which:

FIG. 1A is a diagram of the wild-type FVIII and FV domain structures;

FIG. 1B is a diagram of the inactivation resistant FVIII of the presentinvention;

FIG. 2 is a table showing secretion activity of the A-1 mutated FVIIIproteins of the present invention compared to wild-type FVIII;

FIG. 3 is a graph showing the thrombin activation of APC resistant FVIIIof the present invention and wild-type FVIII;

FIGS. 4A and 4B are photographs of gels showing the expression andthrombin cleavage of the APC resistant FVIII of the present invention;

FIGS. 5A and 5B are photographs of gels showing APC cleavage of the APCresistant FVIII of the present invention;

FIG. 6 is a photograph of a gel showing purified wild-type and APCresistant FVIII of the present invention;

FIGS. 7A and 7B are graphs showing APC-mediated functional inactivationof wild-type and APC resistant FVIII of the present invention;

FIG. 8 is a diagram of the domain structure of the single-chaininactivation resistant FVIII of the present invention;

FIG. 9 is a diagram of the domain structure of the inactivationresistant heterodimer FVIII protein of the present invention;

FIG. 10 is a photograph of a gel showing relative synthesis andsecretion levels of the inactivation resistant FVIII of the presentinvention;

FIG. 11 is a photograph of a gel showing the cleavage patterns of theinactivation resistant FVIII of the present invention;

FIG. 12 is a graph showing the functional activation and inactivation ofthe inactivation resistant FVIII of the present invention as compared towild-type FVIII;

FIG. 13 is a graph showing the activation and reduced rate ofinactivation of immunoaffinity purified inactivation resistant FVIII ofthe present invention as compared to wild-type FVIII;

FIG. 14 is a graph illustrating the results of an ELISA assaydemonstrating antibody-inducible vWF binding of the inactivationresistant FVIII of the present invention;

FIG. 15 is a graph illustrating the results of an ELISA assaydemonstrating antibody-inducible vWF binding of the inactivationresistant FVIII of the present invention following thrombin activation;and

FIG. 16 is a graph illustrating the results of an ELISA assaydemonstrating antibody-inducible vWF binding of the inactivationresistant FVIII of the present invention following thrombin activation,and retained FVIII activity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Novel purified and isolated nucleic acid sequences encodingprocoagulant-active FVIII are provided. Nucleic acid sequences encodingamino acid sequences corresponding to known human FVIII sequences, thatinclude an A1-domain mutation are provided. More specifically, nucleicacid sequences are provided that encode amino acid sequencescorresponding to known human FVIII sequences wherein amino acid residue309, phenylalanine, is mutated. In a preferred embodiment, Phe309 iseither deleted or substituted with any other amino acid residue,preferably serine. The resulting FVIII protein is capable of secretionat levels higher than typically obtained with wild-type FVIII andretains procoagulant activity.

Nucleic acid sequences encoding amino acid sequences corresponding toknown human FVIII sequences containing mutated APC cleavage sites arealso provided. In a preferred embodiment, the APC cleavage sites Arg336and Arg562 are mutated, preferably to isoleucine and lysine,respectively (R336I and R562K). The resulting FVIII protein is APCresistant.

Nucleic acid sequences are also provided which encode amino acidsequences corresponding to known human FVIII sequences, wherein theB-domain is deleted, the von Willebrand factor binding site (i.e., theacidic region of the amino terminus of the light chain) is deleted, athrombin cleavage site is mutated, and an amino acid sequence spacer isinserted between the A2- and A3-domains. This embodiment may furtherinclude an APC cleavage site mutation, for example one or both of theAPC cleavage site mutations described herein. In a preferred embodiment,the thrombin cleavage site Arg740 is mutated, preferably by substitutionwith alanine (R740A) or lysine (R740K). The amino acid sequence spaceris of a sufficient length to allow the protein to be activated bythrombin to achieve a heterodimer, wherein the A2-domain remainscovalently associated with the light chain. In a preferred embodiment,the spacer is approximately 54 residues in length. In another preferredembodiment, the spacer comprises the 54 residues of the amino portion ofthe wild-type FVIII B-domain, i.e. residues 741 to 794, wherein residue794 is threonine or leucine. The single-chain polypeptide (novel FVIII,also referred to herein as IR8) upon activation with thrombin, becomes aheterodimer (novel FVIIIa, also referred to herein as IR8a), having anapproximate five-fold increase in specific activity compared to purifiedwild-type FVIII.

In a further embodiment, the inactivation resistant FVIII of the presentinvention may be employed in combination with an antibody orcross-linking agent which increases the protein's binding affinity tovWF. For example, when the vWF binding site-deleted inactivationresistant FVIII of the present invention is in the presence of ESH8, acommercially available mouse monoclonal antibody (American Diagnostics,Inc. Greenwich, Conn.), which recognizes an epitope at amino acids 2248to 2285 within the C2-domain, the inactivation resistant FVIII binds tovWF. As set forth in greater detail in Example 4, the inactivationresistant FVIII of the present invention has at least a 10-fold reducedaffinity for vWF compared to wild-type FVIII, however, in the presenceof ESH8, it has only a 2-fold reduced affinity for vWF. It has recentlybeen reported that ESH8 can function as an inhibitor of wild-type FVIIIactivation by increasing the affinity of thrombin-cleaved FVIII (FVIIIa)for vWF. Saenko, E. L. et al., Blood 86, Abstract No. 749 (1995). Bydelaying the release of FVIIIa from vWF, A2 dissociation and furtherproteolytic cleavages likely inactivate the FVIIIa before it can fullyrelease from vWF and exert its cofactor function. A human inhibitorantibody that recognizes an epitope at amino acids 2218 to 2307 withinthe C2-domain has also been reported that appears to inhibit wild-typeFVIII activation by a similar mechanism and may similarly be used toinduce vWF binding. Shima, M. et al., Blood 86, Abstract No. 748 (1995)and Shima, M. et al., British J. Hematol. 91: 14-721 (1995).

In yet a further embodiment, the nucleic acid sequences of the presentinvention encode APC resistant FVIII described herein, having anadditional mutation at Phe309. Preferably, Phe309 is deleted orsubstituted with another amino acid, e.g., serine. The nucleic acidsequences of the present invention may also encode inactivationresistant FVIII described herein, also having an additional mutation atPhe309. Again, Phe309 is preferably deleted or substituted with anotheramino acid, e.g., serine. Thus, the nucleic acid sequences of thepresent invention encode FVIII proteins that exhibit inactivationresistance and/or increased secretion.

It will be appreciated that due to the increased specific activity ofthe proteins of the present invention, a lower dosage of protein may beadministered to hemophiliac patients while maintaining therapeuticallyeffective FVIII activity levels. In addition to cost savings, byutilizing the proteins of the present invention in FVIII replacementtherapy, the total exposure of protein to the patient is reduced,thereby lowering the likelihood of inhibitor formation. It will furtherbe appreciated that the proteins of the present invention are alsouseful in gene therapy-related treatment.

DNA sequences for human FVIII are known, as are expression methods (see,e.g. Toole et al., Nature 312:312-317 (1984); Wood et al., Nature312:330-337, Vehar et al., Nature 312:337-342, U.S. Pat. No. 4,757,006,WO 87/04187, WO 88/08035 and WO 88/03558). The novel purified andisolated nucleic acid sequences encoding the FVIII protein of thepresent invention, i.e. a nucleic acid sequence encoding a polypeptidesequence substantially the same as human FVIII or variants thereofmodified as is known in the art and described herein, may be made byconventional techniques. For example, the mutations at Phe309 and theAPC and thrombin cleavage sites may thus be made by site-directedmutagenesis of the cDNA. One of skill in the art will recognize that“mutation” refers to any alteration including but not limited to,substitutions, insertions and deletions. It will further be appreciatedthat the remainder of the FVIII nucleic acid sequence may vary from thewild-type FVIII by containing additional modifications such as thosedisclosed in U.S. Pat. No. 5,004,803, WO 86/06101, and WO 87/07144.FVIII analogs have been developed to better understand the specificstructural requirements for FVIII activatibility, inactivatibility, andin vivo efficacy and are also within the scope of the present invention.Included among the features to be optimized are simplified preparation,ease of administration, stability, improved clearance/distributioncharacteristics, reduced immunogenicity, and prolonged half-life.Moreover, it will be appreciated that variant FVIII nucleic acidsequences in accordance with the present invention also include allelicvariations, i.e. variations in sequence due to natural variability fromindividual to individual, or with other codon substitutions or deletionswhich still retain FVIII-type procoagulant activity.

Alternate nucleic acid forms, such as genomic DNA, cDNA, and DNAprepared by partial or total chemical synthesis from nucleotides, aswell as DNA with mutations, are also within the contemplation of theinvention.

Association of nucleic acid sequences provided by the invention withhomologous or heterologous species expression control sequences, such aspromoters, operators, regulators, and the like, allows for in vivo andin vitro transcription to form mRNA which, in turn, is susceptible totranslation to provide novel FVIII proteins and related poly- andoligo-peptides in large quantities. The present invention thus comprisesthe expression products of the nucleic acid sequences of the invention,as well as activated forms of these expression products. In a presentlypreferred expression system of the invention, FVIII encoding sequencesare operatively associated with a regulatory promoter sequence allowingfor transcription and translation in a mammalian cell to provide, forexample, FVIII having clotting activity.

As used herein the term “procoagulant-active” and “active” FVIII, may beused interchangeably to refer to one or more polypeptide(s) or proteinsdemonstrating procoagulant activity in a clotting assay. The term FVIIImay be used herein to encompass FVIIIa and one skilled in the art willappreciate from the context in which the terms are used which term(pre-thrombin activated FVIII or thrombin activated FVIII (FVIIIa)) isintended. As used herein, the term “polypeptides” includes not only fulllength protein molecules but also fragments thereof which, by themselvesor with other fragments, generate FVIII procoagulant activity in aclotting assay. It will be appreciated that synthetic polypeptides ofthe novel protein products of the present invention are also within thescope of the invention and can be manufactured according to standardsynthetic methods. It will also be appreciated that in the amino acidnumbering system used herein, amino acid residue 1 is the first residueof the native, mature FVIII protein. It will further be appreciated thatthe term “domain” refers to the approximate regions of FVIII, known tothose skilled in the art.

As used herein, the phrase “a sequence substantially corresponding tothe sequence” is meant to encompass those sequences which hybridize to agiven sequence under stringent conditions as well as those which wouldhybridize but for the redundancy of the genetic code and which result inexpression products having the specified activity. Stringent conditionsare generally 0.2×SSC at 65° C. The phrase “substantially duplicative”is meant to include those sequences which, though they may not beidentical to a given sequence, still result in expression product,proteins, and/or synthetic polypeptides that have FVIII activity in astandard clotting assay.

The incorporation of the sequences of the present invention intoprokaryotic and eucaryotic host cells by standard transformation andtransfection processes, potentially involving suitable viral andcircular DNA plasmid vectors, is also within the contemplation of theinvention. Prokaryotic and eucaryotic cell expression vectors containingand capable of expressing the nucleic acid sequences of the presentinvention may be synthesized by techniques well known to those skilledin this art. The components of the vectors such as the bacterialreplicons, selection genes, enhancers, promoters, and the like, may beobtained from natural sources or synthesized by known procedures (see,e.g. Kaufman et al., J. Mol. Biol. 159:601-621 (1982) and Kaufman, PNAS82:689-693 (1995)). Expression vectors useful in producing proteins ofthis invention may also contain inducible promoters or compriseinducible expression systems as are known in the art.

Established cell lines, including transformed cell lines, are suitableas hosts. Normal diploid cells, cell strains derived from in vitroculture of primary tissue, as well as primary explants (includingrelatively undifferentiated cells such as hematopoietic stem cells) arealso suitable. Candidate cells need not be genotypically deficient inthe selection gene so long as the selection gene is dominantly acting.

The use of mammalian host cells provides for such post-translationalmodifications, e.g. proteolytic processing, glycosylation, tyrosine,serine, or threonine phosphorylation, as may be made to confer optimalbiological activity on the expression products of the invention.Established mammalian cell lines are thus preferred, e.g. CHO (ChineseHamster Ovary) cells. Alternatively, the vector may include all or partof the bovine papilloma virus genome (Lusky et al., Cell 36:391-401(1984)) and be carried in cell lines such as C127 mouse cells as astable episomal element. Other usable mammalian cell lines include HeLa,COS-1 monkey cells, melanoma cell lines such as Bowes cells, mouse L-929cells, 3T3 lines derived from Swiss, Balb-c or NIH mice, BHK or HaKhamster cell lines, and the like.

Whichever type of expression vector is used, it may be preferable toco-express the FVIII nucleic acids of the present invention with anucleic acid sequence encoding von Willebrand factor (vWF) or an analogthereof, e.g. as described in WO 87/06101, WO 88/08035 and U.S. Pat. No.5,250,421. It may also be preferred to express the protein in mediacontaining a protease inhibitor such as aprotinin, e.g. in an amountfrom about 0.01 to about 5%, preferably from about 0.5 to about 1.0%,(vol/vol) (Aprot., 15-30 Trypsin inhibitor units (TIU)/ml, Sigma) orcorresponding amounts of activity units of other protease inhibitors.

Stable transformants are screened for expression of the procoagulantproduct by standard immunological or activity assays. The presence ofthe DNA encoding the procoagulant proteins may be detected by standardprocedures such as Southern blotting. Transient expression of theprocoagulant genes during the several days after introduction of theexpression vector into suitable host cells such as COS-1 monkey cells,is measured without selection by activity or immunologic assay of theproteins in the culture medium. Following the expression of the DNA byconventional means, the protein so produced may be recovered, purifiedand/or characterized with respect to physicochemical, biochemical and/orclinical parameters, all by known methods.

In a further embodiment, the nucleotide sequences of the presentinvention may be used in gene therapy applications, e.g. to treathemophilia caused by deficiency of FVIII. Due to the increased specificactivity of the FVIII proteins of the present invention, therapeuticallyeffective FVIII activity may be achieved with lower protein expressionlevels as compared to other forms of FVIII including wild-type FVIII.The methods of this invention thus comprise the step of introducing thenucleotide sequences of the present invention into a target cell. Inorder to effectuate transfer, the nucleotide sequences to be transferredmust be associated with a vehicle capable of transducing the targetcell. Those skilled in the art will appreciate that such vehiclesinclude known gene therapy delivery systems including, but not limitedto, adenoviral, retroviral and adeno-associated viral vectors, as wellas liposomes and DNA-protein complexes.

The invention will be further understood with reference to the followingillustrative examples and procedures, which is purely exemplary, andshould not be taken as limiting the true scope of the present invention.Example 1 describes the preparation and analysis of the A1-domainmutated FVIII of the present invention. Example 2 describes thepreparation and analysis of the APC resistant FVIII of the presentinvention. Example 3 describes the preparation and analysis of theinactivation resistant FVIII of the present invention. Example 4describes the inducible vWF-binding of the inactivation resistant FVIIIof the present invention. Example 5 describes pharmaceuticalcompositions and methods of use of the FVIII proteins and nucleotidesequences of the present invention.

EXAMPLE 1 Preparation and Analysis of A1-Domain Mutated Factor VIII

A statistical algorithm (Blond-Elguindi, S. et al., Cell 75:717-728(1993)) was applied to predict the BiP binding potential of 7-merpeptides to the 226-336 region of FVIII (residue 1 is the first aminoacid residue of the native, mature FVIII protein). Residues Leu303 toPhe309 were found to have a BiP binding score of +14 where any scoreover +10 has an extremely high probability of binding BiP. Fay, P. J. etal., J. Biol. Chem. 266:8957-8962 (1991). This region contains ahydrophobic cluster where 7 of 11 amino acid residues are Leu or Phe.

Initially all 7 Leu and Phe residues in the potential BiP binding pocketwere mutated to Ala. Site-directed mutagenesis by oligonucleotideoverlap-extension polymerase chain reaction (PCR) mutagenesis wasutilized. A FVIII/FV chimeric was produced wherein residues 226-336 ofFVIII were replaced with the homologous residues from FV (residues198-313). Marquette, K. A. et al., J. Biol. Chem. 270:10297-10303(1995). Partially complementary primers that contained the mutation wereutilized with two primers directed at the MluI sites at 226 and 336 inthe FVIII/FV chimeric cDNA to amplify two overlapping products thatcontain the directed mutation. These two fragments were isolated andfused together by PCR using the two MluI site containing primers. Theresultant MluI fragment was then subcloned into the MluI digestedFVIII/FV 226-336 chimera within the expression vector pMT2. Allmutations were confirmed by DNA sequencing over the PCR amplifiedregion. Expression vectors encoding these mutants were transfected intoCOS-1 cells and the conditioned medium taken at 60 hr for analysis ofFVIII activity by Coatest activity assay. When all 7 Leu and Pheresidues in the potential BiP binding pocket were mutated to Ala, themolecule was not secreted. Subsequently, the Phe residues wereindividually mutated to the respective amino acid residues in FV. Thesecretion of the F309S mutants (either alone or in combination withother mutants) were reproducibly increased 2-fold in severaltransfection experiments. As shown in FIG. 2, mutations at otheradjacent residues (F293S, F306W) did not improve secretion. Theincreased secretion of the F309S mutants correlated with a 2-foldincrease in FVIII antigen, indicating a specific activity similar towild-type FVIII. Metabolic labeling with [³⁵S]-methionine for 20 minwith a 4 hr chase in medium containing excess unlabeled methionineindicated that the increased secretion of the F309 and Q,F305/309K,Smutants correlated with increased secretion compared to wild-type FVIII.

Stably transfected CHO cell lines were engineered that express the F309Smutant. Of 35 original transfected CHO cell clones selected fordihydrofolate reductase expression, 5 clones were obtained that expresssignificant levels of FVIII (approximately 1 U/ml/10⁶ cells/day). Two ofthese clones express the same level of FVIII as the original 10A1 cellline that was obtained by screening over 1000 original transfected cellclones. Kaufman, R. J. et al., J. Biol. Chem. 263:6352-6362 (1988).Thus, in low concentrations of methotrexate, the mutation permits highlevel FVIII expression to be obtained more readily.

Further selection in methotrexate is performed to determine if themaximum productivity of FVIII/cell is improved. Experiments areperformed to measure BiP interaction and ATP dependence for secretionfor the F309W/S functional FVIII mutant in the stably transfected CHOcells.

EXAMPLE 2 Preparation and Analysis of APC Resistant Factor VIIIExperimental Procedures

Materials.

FVIII deficient plasma and normal pooled human plasma were obtained fromGeorge King Biomedical, Inc., (Overland Park, Kans.). Monoclonalantibody to the heavy chain of FVIII (F8) coupled to CL4B-sepharose wasused and may be prepared by known methods. Activated partialthromboplastin (Automated APTT reagent) was purchased from GeneralDiagnostics Organon Teknika Corporation (Durham, N.C.). Soybean trypsininhibitor, phenylmethylsulfonylfluoride (PMSF) and aprotinin werepurchased from Boehringer, Mannheim GmbH (Mannheim, Germany). Humaná-thrombin was obtained from Sigma Chemical Co. (St. Louis, Mo.). HumanAPC was purchased from Enzyme Research Laboratories, Inc., (South Bend,Ind.). Dulbecco's modified eagle medium (DMEM), á-modification ofEagle's Medium (á-MEM) and methionine-free DMEM were obtained from GibcoBRL (Gaithersburg, Md.). Fetal bovine serum was purchased from PAALaboratories Inc., (Newport Beach, Calif.).

Plasmid Construction.

Site-directed oligonucleotide-mediated mutagenesis was performed by thegapped-heteroduplex procedure to introduce Arg336Ile (R336I) and/orArg562Lys (R562K) mutations into the FVIII cDNA cloned into theexpression vector pED6, as described previously. Pittman, D. D. et al.,Method in Enzymology Vol. 222 (San Diego, Calif.; Academic Press, Inc.,)p. 236 (1993) and Toole, J. J. et al., PNAS (USA) 83:5939 (1986). Themutations were confirmed by extensive restriction endonuclease digestionand DNA sequence analysis. The resultant molecules were designated R336Ior R562K and the double mutant, referred to herein as APC resistantFVIII, was designated R336I or R562K. In addition, a R336I/K338I doublemutant was also constructed.

Analysis of Synthesis and Secretion.

Plasmid DNA was transfected into COS-1 cells by the diethyl aminoethyl(DEAE)-dextran procedure as described. Pittman, D. D. et al., Method inEnzymology Vol. 222 (San Diego, Calif.; Academic Press, Inc.,) p. 236(1993). Conditioned medium was harvested 60 hours post transfection inthe presence of 10% heat-inactivated fetal bovine serum (FBS) for FVIIIassay. Subsequently, cells were metabolically labeled with[³⁵S]-methionine as described before. Pittman, D. D. et al., Method inEnzymology Vol. 222 (San Diego, Calif.; Academic Press, Inc.,) p. 236(1993). Labeled conditioned medium was harvested and immunoprecipitatedwith F8 antibody coupled to CL-4B sepharose. Immunoprecipitated proteinsfrom the conditioned medium were washed with PBS containing TritonX-100, resuspended 50 mM Tris-HCl pH 7.5, 150 mM NaCl, 2.5 mM CaCl₂ and5% glycerol (buffer A), and were treated with or without 8.5 U/ml ofthrombin at 37° C. for 1 hour. Samples were analyzed by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducingconditions and visualized by autoradiography after fluorography bytreatment with En3hance (Dupont; Boston, Mass.).

Analysis of APC Cleavage of FVIII.

Radiolabeled and immunoprecipitated FVIII was resuspended with buffer Aand treated with 30 ì g/ml of bovine APC in the presence of 100 ì g/mlinosithin and 10 mM CaCl₂ at 37° C. for 1.5 hr. The resultingpolypeptides were separated by SDS-PAGE and visualized byautoradiography as described above.

Generation of CHO Cell Lines and Purification of FVIII.

In order to obtain large amounts of FVIII, stably transfected CHO cellslines were engineered containing DNA encoding the wild-type and APCresistant FVIII. The expression plasmids were digested with Cla1 andtransfected into CHO cells using the lipofection method. Pittman, D. D.et al., Method in Enzymology Vol. 222 (San Diego, Calif.; AcademicPress, Inc.,) p. 236 (1993). Conditioned media were applied to a columnof F8 antibody coupled CL-4B sepharose. The bound FVIII was eluted inbuffer containing 60% ethylene glycol and concentrated by dialysisagainst a 10% polyethylene glycol (MW 15K-20K) containing buffer. Fay,P. J. et al., J. Biol. Chem. (in press) (1996). Concentrated sampleswere dialyzed against modified buffer A containing 5 mM CaCl₂ (bufferB). The FVIII clotting activity of the purified preparations were about20 U/ml. The structure of purified proteins was evaluated by SDS-PAGEand silver staining (Bio-Rad Laboratories; Hercules, Calif.).

FVIII Assay.

FVIII activities were measured in a one stage clotting assay using FVIIIdeficient plasma as substrate. One unit of FVIII activity is the amountmeasured in 1 ml of normal human pooled plasma. For thrombin activation,conditioned medium was diluted into buffer A and incubated at roomtemperature with 1 U/ml thrombin. After incubation for increasingperiods of time, aliquots were diluted and assayed for FVIII activity.

APC Inactivation of FVIII.

Purified FVIII samples diluted to 3 U/ml in buffer B were mixed with 100ì g/ml inosithin and human APC 100 ng/ml or buffer alone as a control.After increasing periods of time at 37° C., aliquots were diluted andthe residual FVIII was determined.

Effect of APC Resistant FVIII in the APC Resistance Assay.

Twenty U/ml of purified FVIII was diluted with FVIII deficient plasma to1 U/ml. These samples were tested by the commercialized APC resistanceassay kit (Coatest APC Resistance; Chromogenix, Molndal, Sweden)according to the manufacturer.

Results

R336I, R562K, and R336I/R562K Mutant FVIII Molecules are EfficientlySecreted with FVIII Activity Similar to Wild-Type FVIII.

The activity and secretion of FVIII mutants were measured by transientDNA transfection of COS-1 monkey cells. The FVIII clotting activity inthe conditioned medium demonstrated that all mutants had FVIII activitysimilar to wild-type FVIII, approximately 300 mU/ml (see Table 1).Thrombin activation of the conditioned medium samples indicated thatthere was no difference in the rate of thrombin activation and decay ofprocoagulant activity. As shown in FIG. 3, all samples were immediatelyactivated (3-5 fold) at 10 seconds after thrombin addition and wereimmediately inactivated. In FIG. 3, the symbols represent wild-typeFVIII (X), R336I (•), R562K (⋄) and R336I/R562K (

). To measure FVIII secretion, transfected cells were metabolicallylabeled with [³⁵S]-methionine for 2 hr and then chased for 4 hr inmedium containing excess unlabeled methionine. The secreted proteinswere analyzed by immunoprecipitation of labeled conditioned medium. Asshown in FIG. 4A, wild-type FVIII and all mutants were secreted atsimilar levels as a 300 kDa single chain and a 200 kDa heavy chain andan 80 kDa light chain. As shown in FIG. 4B, thrombin cleavage for allmolecules generated the light chain migrating at 73 kDa and the heavychain derived fragments corresponding to the 50 kDa A1-domain and 43 kDaA2-domain as expected (FIG. 4B). In addition, for wild-type FVIII andR562K (FIG. 4B, lanes 7 and 9) there was some cleavage at residue 336 toyield a 45 kDa species. In contrast, R336I and R336I/R562K (FIG. 4B,lanes 8 and 10) mutants did not generate the 45 kDa species, indicatingthat isoleucine mutation at residue 336 is resistant to cleavage byexcess thrombin. For FIGS. 4A and 4B, the molecular size markers areshown on the left, “Mock” represents cells that did not receive DNA, andsc, hc and lc represent single chain, heavy chain and light chain,respectively. TABLE 1 FVIII Clotting Activity in Conditioned Medium FromTransfected COS-1 Cells FVIII Clotting Activity (mU/ml) (n = 5)Wild-type 318.8 ± 36.3 R336I 306.4 ± 51.2 R562K 340.0 ± 44.8 R336I/R562K308.4 ± 76.9data represents mean ± SD

R562K is Completely Resistant and R336I is Mostly Resistant to APCCleavage at the Mutated Site.

APC cleavage of FVIIIa was evaluated by treating [³⁵S]-methioninelabeled immunoprecipitated FVIII with APC. Analysis of APC cleavageproducts of wild-type FVIII analyzed by SDS-PAGE on a 5-15% gradient geldetected the heavy chain fragments of 50 kDa and 45 kDa representing theA1-domain, and of 43 kDa representing the A2-domain, that were notpresent in the conditioned medium of cells that did not receive DNA. Asshown in FIG. 5A, lane 2, a lower molecular weight product at 25 kDa wasdetectable, representing the carboxy-terminus of A2-domain. As shown inFIG. 5A, lane 3, R336I FVIII was partially resistant to cleavage atresidue 336, as indicated by an increase in the 50 kDa and a reductionof the 45 kDa cleavage products compared to wild-type. The R336Idisplayed no change in the amount of the 25 kDa species indicatingefficient cleavage at residue 562. As shown in FIG. 5A, lane 4, R562Kmutant FVIII was resistant to cleavage at residue 562 as indicated bythe increase in the 43 kDa fragment and loss of the 25 kDa fragment.However, the R562K mutant was efficiently cleaved at 336 as indicated byan intense 45 kDa fragment. APC treatment of the R336I/R562K doublemutant yielded an increase in the 50 kDa and 43 kDa species, and thereduction of 45 kDa and loss of 25 kDa species compared to wild-typeFVIII (see FIG. 5A, lane 5). The migration of the 45 kDa fragmentderived from APC cleavage of the R336I mutant was slightly reduced uponanalysis by SDS-PAGE on an 8% polyacrylamide gel (see FIG. 5B, comparelanes 7 and 8). In order to determine whether this mutant may be cleavedat the adjacent lysine at residue 338, an R336I and K338I double mutantwas made by site-directed mutagenesis. The R336I/K338I mutant did notgenerate the 45 kDa fragment upon APC digestion (see FIG. 5B, lane 9).In FIGS. 5A and 5B, molecular size markers are shown on the left and“Mock” represents cells that did not receive DNA.

Mutagenesis at Both Arg336 and Arg562 in FVIII are Required forResistance to APC Inactivation.

von Willebrand Factor (vWF) inhibits APC inactivation of FVIII. Koedam,J. A. et al., J. Clin. Invest. 82:1236 (1988) and Fay, P. J. et al., J.Biol. Chem. 266:2172 (1991). Therefore, to study APC inactivation,stably transfected CHO cells that express wild-type and the APC cleavagesite mutants FVIII molecules were engineered. Conditioned medium wascollected for FVIII purification. As shown in FIG. 6, analysis of thepurified proteins by SDS-PAGE under reducing conditions and silverstaining demonstrated that all molecules have similar polypeptidecompositions of heavy chain (hc) and light chain (lc) with minimaldegradation and absence of vWF. These purified proteins were thenanalyzed for functional inactivation by APC. As shown in FIG. 7A, theactivity of all samples, except the R336I/R562K (z,901 ) double mutant,were reduced to 80% after 10 min incubation at 37° C. in the absence ofAPC and were subsequently stable for 60 min thereafter. In the presenceof APC, wild-type FVIII (X) had residual activity of 38% at 10 min and8% at 60 min. In the presence of APC, the inactivation of R336I (•) andR562K (⋄) single mutants were similar and both slower than wild-typeFVIII. After 60 min 41% and 30% of initial activity remained for theR336I and R562K mutants, respectively. In contrast, the R336I/R562K (

) double mutant was resistant to inactivation and retained 76% activityafter 60 min. The results thus demonstrate that the R336I/R562K doublemutant was mostly resistant and both single mutants were only partiallyresistant to APC inactivation.

Ability of APC Resistance Assay Kit to Detect APC Resistant FVIII.

Presently, a commercially available APC resistance assay kit (CoatestAPC Resistance; Chromogenix, Molndal, Sweden) is used to screen theplasma of patients with thrombotic disease associated with the FV R506Qmutation. The ability of this kit to detect APC resistant FVIII wastested by reconstitution of FVIII deficient plasma with either purifiedwild-type or purified mutant FVIII. The APC resistance ratio wascalculated by the measure of the clotting time in the presence of APCdivided by the clotting time in the absence of APC (see Table 2). Onlythe R336I /R562K double mutant demonstrated a lower APC resistance ratiothan 2, a value indicative of an APC resistance phenotype. Svensson, P.J. et al., N. Engl. J. Med. 336:517 (1994). TABLE 2 APC-Resistance Ratioof Wild-Type FVIII and Mutants in the Commercialized Assay KitAPC-Resistance Ratio (n = 3) Wild-type 2.13 ± 0.06 R336I 2.10 ± 0.00R562K 2.13 ± 0.06 R336I/R562K 1.73 ± 0.06data represents mean ± SD

Discussion

All mutants were efficiently secreted from COS-1 cells with a FVIIIactivity similar to wild-type FVIII. Analysis of APC cleavage wasperformed by [³⁵S]-methionine labeling of protein and analysis of FVIIIin the conditioned medium after immunoprecipitation. The R336I mutantwas partially resistant to cleavage at residue 336, but was sensitive tocleavage at Arg562. On the other hand, the R562K mutant was completelyresistant to cleavage at residue 562, but was sensitive to cleavage atArg336. These results indicate that either single mutation at Arg336 orArg562 affects cleavage at the mutated site and that there is not arequired order for APC cleavage at these two sites in FVIII. The doublemutant R336I/R562K was partially resistant to cleavage at residue 336and completely resistant at residue 562. The cleavage of R336I likelyoccurred at an adjacent residue, Lys 338, since a double mutantR336I/K338I was completely resistant to cleavage at this site. Theseresults show that APC cleavage of FVIII can be ragged, i.e. it does nothave a stringent spacing requirement for cleavage.

Analysis of the kinetics of APC cleavage in FVIII indicated that Arg562was preferentially cleaved compared to Arg336 and this initial cleavagemost closely correlated with the loss of cofactor activity. Fay, P. J.et al., J. Biol. Chem. 266:20139 (1991) The slower inactivation of theR562K single mutant as a consequence of cleavage resistance at residue562 is consistent with the hypothesis, and that the resultantinactivation was due to cleavage at Arg336. However, the R336I singlemutant was only partially inactivated by cleavage at Arg562. It has beenshown that both single cleavage site mutants were inactivated at similarrates under the conditions described herein. Assuming that cleavage atArg336 and Arg562 occur at the same time, the effect of cleavage ateither Arg336 or Arg562 for inactivation of FVIII appear to be similar.The rapid inactivation of wild-type FVIII may be due to synergisticroles of cleavage at Arg336 and Arg562 for inactivation of FVIII.

At present, there are no reports describing patients with mutations inthe APC cleavage sites of FVIII. To evaluate whether these mutationswould have an APC resistance phenotype, the APC resistant FVIIImolecules were tested in the commercially available APC resistance assaykit (Coatest APC Resistance; Chromogenix, Molndal, Sweden). Only theR336I/R562K double mutant demonstrated a lower APC-resistance ratio.This assay kit can not therefore, detect either single APC cleavage sitemutants of FVIII. In contrast to FVIII, both FV APC single cleavage sitemutants, Arg306Gln and Arg506Gln, showed reduced APC-resistance ratiosin this assay. The results thus show that the commercially available APCresistance kit will not detect FVIII APC resistant mutants unless bothAPC cleavages are inhibited.

EXAMPLE 3 Preparation and Analysis of Inactivation Resistant Factor VIIIExperimental Procedures

Materials.

Anti-heavy chain factor VIII monoclonal antibody (F-8), F-8 conjugatedto CL-4B Sepharose and purified recombinant factor VIII protein wereobtained from Genetics Institute Inc. (Cambridge, Mass.). Anti-human vWFhorseradish peroxidase(HRP)-conjugated rabbit antibody was obtained fromDako Corp. (Carpinteria, Calif.). Anti-light chain factor VIIImonoclonal antibodies, ESH-4 and ESH-8, were obtained from AmericanDiagnostica, Inc., (Greenwich, Conn.). Factor VIII-deficient and normalpooled human plasma were obtained from George King Biomedical, Inc.(Overland Park, Kans.). Activated partial thromboplastin (Automated APTTreagent) and CaCl₂ were obtained from General Diagnostics OrganonTeknika Corporation (Durham, N.C.). Human thrombin, soybean trypsininhibitor, phenylmethylsulfonylfluoride and aprotinin were obtained fromBoehringer, Mannheim GmbH (Mannheim, Germany). O-phenylendiaminedihydrochloride (OPD) was obtained from Sigma Chemical Co. (St. Louis,Mo.). [³⁵S]-methionine(>1000 Ci/mmol) was obtained from Amersham Corp.(Arlington Heights, Ill.). En³Hance was obtained from Dupont (Boston,Mass.). Fetal bovine serum was obtained from PAA Laboratories Inc.(Newport Beach, Calif.). Dulbecco's modified Eagle's medium (DMEM),methionine-free DMEM, OptiMEM, Biotin N-hydroxy succinimide ester, andstreptavidin-horseradish peroxidase conjugate were obtained from GibcoBRL (Gaithersburg, Md.).

Plasmid Mutagenesis.

Mutagenesis was performed within the mammalian expression vectorpMT₂(37) containing the FVIII cDNA(pMT₂VIII). Mutant plasmids weregenerated through oligonucleotide site-directed mutagenesis utilizingthe polymerase chain reaction (PCR). For a detailed description ofoligonucleotide-directed mutagenesis, see Smith, M., Annu. Rev. Genet.19:423 (1985).

Construction 1—90/73 R740K.

Vector pMT₂90/73 was used as the DNA template. The 90/73 construct isdescribed in Nesheim, M. et al., J. Biol. Chem. 266: 17815-17820 (1991)and Pittman, D. et al., Blood 70, Abstract No. 392 (1987). Generally,the 90/73 construct is wild-type FVIII cDNA sequence in which theB-domain and the vWF binding site (acidic region of the light chain)have been deleted (del 741-1689). Oligonucleotide-directed mutagenesiswas used to create a PCR fragment, KpnI/R740K/ApaI, and was ligated intoKpnI/ApaI digested pMT₂90/73.

Construction 2—90/b/73 R740K.

Vector pMT₂VIII was used as the DNA template. Oligonucleotide-directedmutagenesis was used to create a PCR fragment, KpnI/b/1689 MluI (where brepresents a DNA sequence encoding for amino acid residues 741 to 793 ofthe wild-type sequence followed by an MluI site predicting amino acidsthreonine and arginine at residues 794 and 795/1689), which was ligatedinto KpnI/MluI digested vector PMT₂ VIII/1689/MluI. The following aminoacid sequence (and nucleotide sequence encoding same) is the preferredamino acid sequence spacer, wherein residue 794 may be threonine orleucine and is preferably threonine:

Construction 3—90/b/73 R740A.

Vector 90/b/73 was used as the DNA template (wherein b is describedabove and encodes threonine at residue 794). Oligonucleotide-directedmutagenesis was used to create a PCR fragment, KpnI/R740A/b/ApaI, whichwas ligated into KpnI/ApaI digested pMT₂90/73.

Construction 4—90/b/73 R740A/R1689A (DM1).

Vector 90/b/73 R740A was used as the DNA template (wherein b isdescribed above and encodes leucine at residue 794).Oligonucleotide-directed mutagenesis was used to create PCR fragment,KpnI/R740A/b/R1689A/ApaI, which was ligated into KpnI/ApaI digestedpMT₂90/73.

Construction 5—90/b/73 R336I/R740A (DM2).

Vector PMT₂VIII/R336I was digested with SpeI and KpnI. The fragment wasligated into SpeI/KpnI digested 90/b/73 R740A (wherein b is describedabove and encodes threonine at residue 794).

Construction 6—90/b/73 R336I/R562K/R740A (IR8).

Vector PMT₂VIII/R562K was digested with BglII and KpnI. TheBglII/R562K/KpnI fragment was ligated into BglII/KpnI digested 90/b/73R336I/R740A (wherein b is described above and encodes threonine atresidue 794).

The plasmid containing the wild-type FVIII cDNA sequence was designatedFVIII WT. All plasmids were purified by centrifugation through cesiumchloride and characterized by restriction endonuclease digestion and DNAsequence analysis.

DNA Transfection and Analysis.

Plasmid DNA was transfected into COS-1 cells by the DEAE-dextran method.Conditioned medium was harvested at 64 hours post-transfection in thepresence of 10% fetal bovine serum. FVIII activity was measured byone-stage APTT clotting assay on a MLA Electra 750. Protein synthesisand secretion were analyzed by metabolically labeling cells at 64 hourspost-transfection for 30 minutes with [³⁵S]-methionine (300 mCi/ml inmethionine-free medium), followed by a chase for 4 hours in mediumcontaining 100-fold excess unlabeled methionine and 0.02% aprotinin.Cell extracts and conditioned medium containing labeled protein wereharvested. WT and mutant FVIII proteins were immunoprecipitated fromequal proportions of cell extract and conditioned medium with F-8coupled to CL-4B Sepharose. Immunoprecipitates were washed andresuspended in Laemmli sample buffer. Samples were analyzed byelectrophoresis on a reducing SDS-low bis-8% polyacrylamide gel. Thegels were treated with En³Hance and the proteins visualized byautoradiography.

Protein Purification.

Partially purified IR8 protein was obtained from 200 mls of conditionedmedium from transiently transfected COS-1 cells by immunoaffinitychromatography. Partially purified FVIII WT protein was obtained from200 mls of conditioned medium from stably transfected CHO cells andimmunoaffinity purified in the same manner. The proteins eluted into theethylene glycol-containing buffer were dialyzed and concentrated againsta polyethylene glycol (MW˜15-20,000)-containing buffer and stored at−70° C.

FVIII Activity Assay.

FVIII activity was measured in a one-stage APTT clotting assay byreconstitution of human FVIII-deficient plasma. For thrombin activation,protein samples were diluted into 50 mM Tris-HCl pH 7.5, 150 mM NaCl,2.5 mM CaCl₂ and 5% glycerol, and incubated at room temperature with 1U/ml thrombin. After incubation for increasing periods of time, aliquotswere diluted and assayed for FVIII activity. One unit of FVIII activityis the amount measured in 1 ml of normal human pooled plasma.

FVIII Antigen Determination.

FVIII antigen was quantified using a sandwich ELISA method utilizinganti-light chain antibodies ESH-4 and ESH-8. Purified recombinant FVIIIprotein was used as a standard.

Results

Generation of FVIII Inactivation Resistance.

All of the above constructs are based upon 90/73, wherein the B-domain(residues 795 to 1647) and the vWF binding site (residues 1648 to 1688,also referred to as the acidic region of the amino terminus of the lightchain), have been deleted. Nesheim, M. et al., J. Biol. Chem. 266:17815-17820 (1991) and Pittman, D. et al., Blood 70, Abstract no. 392(1987). FIG. 8 sets forth the domain structures of wild-type FVIII andthe above constructs as well as the mutations at the APC and thrombincleavage sites. As described herein and in FIG. 8, “b” represents theamino acid sequence spacer which is of a sufficient length to allow theprotein to be activated by thrombin to achieve a heterodimer, whereinthe A2-domain remains covalently associated with the light chain. In apreferred embodiment, the amino acid sequence spacer is preferably theamino portion of the wild-type B-domain, i.e. amino acid residues 741 to793 followed by an MluI site (for cloning purposes) predicting aminoacids threonine or leucine, preferably threonine, at residue 794 andarginine at 795/1689.

FIG. 8 sets forth a model of activation of the constructs of the presentinvention. Wild-type FVIII and the mutant 90/73 both achieve aheterotrimer upon thrombin activation. When an amino acid sequencespacer is introduced between the A2- and A3-domains of 90/73 containinga mutation at the thrombin cleavage site(del795-1688/Arg336Iso/Arg562Lys/Arg740Ala), upon activation withthrombin, cleavage only occurs after Arg372, generating a FVIIIaheterodimer. This novel FVIII protein designated IR8, maintains stableactivity following thrombin activation.

Synthesis and Secretion of IR8.

FVIII WT and the various inactivation-resistance mutants were comparedby transient DNA transfection of the cDNA expression vectors into COS-1monkey cells. At 60 hours following transfection, the rates of synthesiswere analyzed by immunoprecipitation of cell extracts from[³⁵S]-methionine pulse-labeled cells. Intracellular FVIII WT wasdetected in its single chain form and migrated at approximately 250 kDa(FIG. 10, lane 1). The mutant 90/80 is a BDD FVIII mutant (del741-1648)previously characterized, that migrates at ˜170 kDa and demonstrates anincreased intensity from pulse-labeled cell extracts consistent withincreased efficiency of synthesis (FIG. 10, lane 3). 90/73 migratesslightly faster due to the additional deletion of the residues of theacidic region (FIG. 10, lane 5). All the 90/b/73 based constructsincluding IR8 exhibited similar band intensity to the 90/80 and 90/73constructs suggesting that the multiple missense mutations did notinterfere with efficient protein synthesis. Additional bands within thecell extract are not observed in mock cell extract immunoprecipitatedwith an anti-FVIII specific antibody and represent both FVIII specificproteins and co-immunoprecipitating intracellular proteins. Following a4 hour chase period, the majority of FVIII WT is lost from the cellextract (FIG. 10, lane 2) and can be recovered from chase conditionedmedium in its 280 kDa single chain, 200 kDa heavy chain and 80 kDa lightchain forms (FIG. 10, lane 3). Although all of the BDD andinactivation-resistance mutants demonstrated significant amounts oftheir primary translation products remaining within the cell extractfollowing the 4 hour chase (FIG. 10, lanes 4, 6, 8, 10, 12), they wereall recovered from the chase conditioned medium as single chain species(FIG. 11, lanes 5, 7, 9, 11, 13). Therefore the various alterations ofthe FVIII construct did not have significant impact on secretion.

Structural Stability of IR8 Following Thrombin Cleavage.

The labeled FVIII proteins immunoprecipated from the chase conditionedmedium were incubated with thrombin (1 U/ml) for 30 minutes prior toSDS-PAGE analysis. FVIII WT was efficiently cleaved into a heterotrimerof fragments consisting of a 50 kDa A1 subunit, 43 kDa A2 subunit and 73kDa thrombin-cleaved light chain, A3-C1-C2 (FIG. 11, lane 4). 90/73 WTwas also cleaved into a heterotrimer of subunits similar to FVIII WT(FIG. 11, lane 6) consistent with previous observations and depicted inFIG. 1A. 90/73 Arg740Lys generated a heterodimer of thrombin-cleavedsubunits consistent with a 50 kDa A1 subunit and an A2-A3-C1-C2 fusedlight chain (FIG. 11, lane 8). 90/b/73 Arg740Lys demonstrated thrombincleavage fragments consistent with 2 heteromeric species, a 50 kDaA1/120 kDa A2-b-A3-C1-C2 heterodimer, as well as a 43 kDa A2 subunit andan ˜85 kDa fragment consistent with a b-A3-C1-C2 fused light chain (FIG.11, lane 10). The appearance of the A2 subunit following incubation withthrombin suggested that Lys740 did not completely abrogate thrombincleavage in the presence of the b spacer. With the more radical missensemutation to Ala740, a stable heterodimeric species was demonstrated(FIG. 11, lane 12). This stable heterodimeric structure followingthrombin cleavage was maintained for IR8 with additions of the missensemutations Arg336Iso and Arg562Lys (FIG. 11, lane 14).

Functional Stability of IR8 Following Thrombin Activation.

Having demonstrated the structural integrity of the IR8 heterodimer uponthrombin cleavage, the functional consequence of this modification onactivation and inactivation was examined in an in vitro functionalassay. Immunoaffinity purified FVIII WT and IR8 were incubated withthrombin and assayed for FVIII activity by a one stage APTT clottingassay. An example of the functional activation and inactivation isdepicted in FIG. 12 and is typical of multiple repeat experiments. Underthese conditions, FVIII WT was maximally activated within the first 10seconds of incubation with thrombin, then rapidly inactivated over thenext 5 minutes. IR8 did not reach peak activity until 30 secondsincubation with thrombin, suggesting a modestly reduced sensitivity tothrombin activation compared to FVIII WT. In addition, the peak activityfor thrombin activated IR8 was lower (74.7+6.7% of peak thrombinactivated FVIII WT activity, n=3), suggesting some reduced efficiency asa cofactor. However, IR8 demonstrated significant retention of peakactivity over the first 10 minutes of incubation with thrombin(66.9+5.3% of peak IR8 activity, n=3), a period in which FVIII WT wasalmost completely inactivated. Although there is a gradual loss of peakIR8 activity with prolonged incubation with thrombin, IR8 still retained˜38% of peak activity after 4 hours incubation with thrombin.

IR8 Demonstrates Increased FVIII Specific Activity In Vitro.

Immunoaffinity purified FVIII WT and IR8 were assayed for FVIII activityutilizing a standard one stage APTT clotting assay, wherein the firsttime point was 10 seconds. Antigen determinations were made utilizing aFVIII light chain based ELISA. FIG. 13 shows the activation and reducedrate of inactivation expressed as specific activity. The specificactivity values for IR8 were calculated based on a correction for itsmolecular weight. IR8 was observed to have a 5-fold increased specificactivity compared to FVIII WT (102±43 vs. 18.6±7.4 U/mg of protein).

EXAMPLE 4 Inducible vWF-Binding of Inactivation Resistant Factor VIIIExperimental Procedures

Immulon 2 microtiter wells (Dynatech Laboratories, Inc., Chantilly, Va.)were coated with FVIII antibody at a concentration of 2 ì g/ml overnightat 4° C. in a buffer of 0.05 M sodium carbonate/bicarbonate pH 9.6.Wells were washed with TBST (50 mM Tris HCL/pH 7.6, 150 mM NaCl, 0.05%Tween 20) then blocked with 3% bovine serum albumin (BSA) in TBST.Protein samples were diluted in TBST, 3% BSA, 1% factor VIII-deficienthuman plasma+/−ESH8 (molar ratio of ESH8:FVIII protein=2:1). Sampleswere incubated for 2 hours at 37° C. in 1.7 ml microfuge tubes. Sampleswere then incubated for an additional 2 hours in the blocked and washedmicrotiter wells. Wells were then washed in TBST containing 10 mM CaCl₂.Anti-vWF-HRP antibody was diluted in TBST, 3% BSA, 10 mM CaCl₂ andincubated in the wells for 2 hours at 37° C. Following additionalwashing with TBST containing 10 mM CaCl₂, OPD substrate was added to thewells and incubated for 3 minutes. The color reaction was stopped with 2M H₂SO₄ and the optical density (O.D.) read at 490 nm using an EL 340automated microplate reader (Biotek Instruments Inc., Winooski, Vt.).

Results

FIG. 14 shows the results of the FVIII-vWF binding ELISA. An anti-A2domain trap was used. After a 4 hour incubation with FVIII-deficientplasma (1:100 dilution), binding was detected by perioxidase conjugatedanti-vWFab. As shown in FIG. 14, a 10-fold lower binding affinity of IR8to vWF is observed in the absence of ESH8 compared to wild-type FVIII,and a 2-fold lower binding affinity is observed in the presence of ESH8.

FIG. 15 shows the results of the FVIII-vWF binding ELISA with thrombin(IIa) and/or ESH8. The same ELISA method was used however a 2-fold molarexcess of ESH8 was employed as well as a 4 hour incubation with IIa (1U/ml) in the presence of FVIII deficient plasma. As shown in FIG. 15,IR8 retains activity for vWF after thrombin activation suggesting thatthe heterodimer is intact after thrombin cleavage and ESH8 stabilizesthe light chain confirmation such that it retains some affinity for vWF.

Since the binding assays described above utilize a “trap” antibody thatonly recognizes the A2-domain of FVIII, it will only detect FVIII-vWFcomplexes that recognize the A2-domain in association with the rest ofthe protein. Therefore, following the 4 hour incubation of the proteinin the presence of excess thrombin, FVIII wild-type will not only havebeen fully activated but it will have also have been completelyinactivated through A2 dissociation and/or further proteolyticcleavages, and will no longer associate with vWF in a complex that willbe recognized by this assay. The inactivation resistant FVIII of thepresent invention thus retains inducible binding even following completeactivation by thrombin.

It was also shown that the inducible vWF-binding form of theinactivation resistant FVIII of the present invention retained activity.In this assay, an anti-vWF antibody was used as the “trap” for theELISA. The same incubation was performed in the presence and absence ofthrombin and ESH8. Following immobilization of the FVIII-vWF complex onthe plate, FVIII activity was measured using a chromogenic FVIII assaykit (Coamatic, Pharmacia Hepar, Franklin, Ohio) within the ELISA wells.As shown in FIG. 16, following activation by thrombin, no demonstrablyactive FVIII-vWF complexes were observed for FVIII wild-type. However,the inactivation resistant FVIII still had detectable activity under thesame conditions. This suggests that following thrombin activation, theinactivation resistant FVIII is cleaved to a heterodimer of A1 inassociation with a modified light chain of A2-b-A3-C1-C2 that hasESH8-inducible binding to vWF, and retains FVIII activity.

The functional impact of this ESH8-induced IR8-vWF complex was alsoevaluated by assaying for FVIII activity via APTT (Table 3). In theabsence of ESH8, immunoaffinity purified FVIII WT and IR8 demonstratedminimal loss of activity over a 4 hour incubation at 37° C. withFVIII-deficient plasma. In the presence of ESH8, FVIII WT activity wasinhibited by approximately 70%, whereas IR8 retained 100% of its initialactivity. These results suggest that inactivation of WT FVIII in thepresence of ESH8 may be due to A2 subunit dissociation and IR8 isresistant to inactivation by ESH8 because it is not susceptible to A2subunit dissociation. TABLE 3 ESH8 Does Not Inhibit IR8 Activity InPresence Of vWF % Of Initial Activity Protein −ESH8 +ESH8 FVIII WT  92 ±3  29 ± 13 IR8 101 ± 2 120 ± 27

EXAMPLE 5 Pharmaceutical Compositions and Use Pharmaceutical Composition

The FVIII proteins of the present invention can be formulated intopharmaceutically acceptable compositions with parenterally acceptablevehicles and excipients in accordance with procedures known in the art.The pharmaceutical compositions of this invention, suitable forparenteral administration, may conveniently comprise a sterilelyophilized preparation of the protein which may be reconstituted byaddition of sterile solution to produce solutions preferably isotonicwith the blood of the recipient. The preparation may be presented inunit or multi-dose containers, e.g. in sealed ampoules or vials.

Such pharmaceutical compositions may also contain pharmaceuticallyacceptable carriers, diluents, fillers, salts, buffers, stabilizers,and/or other materials well known in the art. The term “pharmaceuticallyacceptable” means a non-toxic material that does not interfere with theeffectiveness of the biological activity of the active ingredient(s).The characteristics of the carrier or other material will depend on theroute of administration.

The amount of FVIII protein in the pharmaceutical composition of thepresent invention will depend upon the nature and severity of thecondition being treated, and on the nature of the prior treatments whichthe patient has undergone. Ultimately, the attending physician willdecide the amount of protein with which to treat each individualpatient. The duration of intravenous therapy similarly will vary,depending on the severity of the disease being treated and the conditionand potential idiosyncratic response of each individual patient.

In addition, the nucleotide sequences encoding the FVIII proteins of thepresent invention may be associated with a gene therapy delivery systemin accordance with procedures known in the art. Such delivery systemsinclude, without limitation, adenoviral, retroviral and adeno-associatedviral vectors, as well as liposomes and DNA-protein complexes. Thesequences of the present invention are contained in oroperatively-linked to such delivery systems in a manner which allows fortranscription, e.g., through the use of sufficient regulatory elements.It will be appreciated that a variety of strategies and methodology forcreating such gene therapy delivery systems are well known to thoseskilled in the art.

Methods of Use

Pharmaceutical compositions containing the proteins of the presentinvention may be used to treat patients suffering from hemophilia causedby deficiency of FVIII.

In practicing the method of treatment of this invention, atherapeutically effective amount of FVIII protein is administered to amammal having a hemophiliac condition caused by FVIII deficiency. Theterm “therapeutically effective amount” means the total amount of eachactive component of the method or composition that is sufficient to showa meaningful patient benefit, i.e. cessation of bleeding.

Administration of the proteins of the present invention can be carriedout in a variety of conventional ways. Intravenous administration to thepatient is preferred. When administered by intravenous injection, theproteins of the invention will be in the form of pyrogen-free,parenterally acceptable aqueous solutions. A preferred pharmaceuticalcomposition for intravenous injection should contain, in addition to theproteins, an isotonic vehicle such as sodium chloride injection,Ringer's injection, dextrose injection, dextrose and sodium chlorideinjection, lactated Ringer's injection, or other vehicles as known inthe art. The pharmaceutical composition according to the presentinvention may also contain stabilizers, preservatives, buffers,anti-oxidants, or other additives known to those of skill in the art.

For cutaneous or subcutaneous injection, the proteins of the presentinvention will be in the form of pyrogen-free, parenterally acceptableaqueous solutions. The preparation of such parenterally acceptableprotein solutions, having due regard to pH, isotonicity, stability, andthe like, is within the skill in the art.

As with the pharmaceutical compositions containing the proteins of thepresent invention, gene therapy delivery systems or vehicles containingnucleotide sequences of the present invention may also be used to treatpatients suffering form hemophilia caused by deficiency of FVIII. Atherapeutically effective amount of such gene therapy delivery vehiclesis administered to a mammal having a hemophiliac condition caused byFVIII deficiency. It will be appreciated that administration of thevehicles of the present invention will be by procedures well establishedin the pharmaceutical arts, e.g. by direct delivery to the target tissueor site, intranasally, intravenously, intramuscularly, subcutaneously,intradermally and through oral administration, either alone or incombination. It will also be appreciated that formulations suitable foradministration of the gene therapy delivery vehicles are known in theart and include aqueous and non-aqueous isotonic sterile injectionsolutions and aqueous and non-aqueous sterile suspensions.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

All patents and other publications cited herein are expresslyincorporated by reference.

1. A procoagulant-active FVIII protein comprising a human FVIIIpolypeptide that is modified, wherein the modification comprises asubstitution of the Arg residue at position 336 with Ile and asubstitution of the Arg residue at position 562 with Lys.
 2. The proteinof claim 1, wherein the modification further comprises a mutation atPhe309.
 3. A nucleic acid molecule comprising a nucleotide sequence thatencodes the protein of claim
 1. 4. A pharmaceutical compositioncomprising an effective amount of the protein of claim 1 in admixturewith a parenterally acceptable vehicle or excipient.
 5. An expressionvector comprising the nucleic acid molecule of claim
 3. 6. A host celltransformed or transfected with the nucleic acid molecule of claim
 3. 7.A method for the production of a procoagulant-active protein comprisingthe steps of: a) growing, in culture, a host cell transformed ortransfected with the nucleic acid molecule of claim 3; and b) isolatingfrom the host cell and culture, the polypeptide product of theexpression of the nucleic acid molecule.